Driving is inarguably a highly visual task. A large body of work has found that drivers with visual sensory impairments (e.g. impaired contrast sensitivity, visual field defects) and/or higher order visual- cognitive processing deficits (e.g. slowed visual processing speed, impaired divided attention) are at increased risk for collision involvement as indicated by accident reports obtained from state licensing agencies. Essential to a comprehensive understanding of the role of vision in driver safety is how the driver's visual capacities ? both visual sensory and visual-cognitive skills ? impact vehicle control and behaviors before and during a vehicle crash. While accident reports provide a wealth of information about the circumstances of a crash (e.g., place, weather conditions, vehicles involved), they tell us little to nothing about the visual mechanisms underlying the occurrence of a crash. In this research plan we implement an innovative approach to study vision and driver safety -- using naturalistic driving data, which avoids the methodological pitfalls associated with accident reports. Naturalistic driving data are generated by participants driving their own vehicles in the course of their everyday life for a year or greater. Their vehicles are unobtrusively equipped with sensors and video cameras, which record vehicle kinematics, GPS location, presence of near-by objects, driver behavior, and the roadway environment. Naturalistic data provide an unprecedented level of objective detail on safety critical events such as crashes and near-crashes including pre- and peri-crash information about driver behavior and contextual factors. We propose to use an existing data source, the Strategic Highway Research Program 2 (SHRP2) Naturalistic Driving Study. SHRP2 collected naturalistic driving data on 3,541 drivers aged 16-98 years old containing 35 million vehicle miles of travel. Specific aims in our research plan will examine associations between crash and near-crash involvement and both visual sensory function and visual- cognitive function, adjusted for age, mileage, and other potential confounders. We will further examine how associations between visual function and crash and near-crash events are modified by the driver's involvement in potentially distracting secondary tasks, risk-taking characteristics, age, and situational on- road characteristics. This research plan will contribute to our knowledge of how visual impairment and distracting behaviors while driving contribute to actual on-road safety and motor vehicle collisions. This information will be invaluable in designing interventions and countermeasures to enhance driver safety in the US and worldwide by elucidating modifiable factors that are associated with increased collision risk.